Tripath Technology, Inc. - Preliminary Information
Over- and Under-Voltage Protection
The TDA1400 senses the power rails through external resistor networks connected to VNNSENSE and
VPPSENSE. The over- and under-voltage limits are determined by the values of the resistors in the
networks, as described in the table “Test/Application Circuit Component Values”. If the supply voltage
falls outside the upper and lower limits determined by the resistor networks, the TDA1400 shuts off the
output stages of the amplifiers. The removal of the over-voltage or under-voltage condition returns the
TDA1400 to normal operation. Please note that trip points specified in the Electrical Characteristics table
are at 25°C and may change over temperature.
The TDA1400 has built-in over and under voltage protection for both the VPP and VNN supply rails. The
nominal operating voltage will typically be chosen as the supply “center point.” This allows the supply
voltage to fluctuate, both above and below, the nominal supply voltage.
VPPSENSE (pin 40) performs the over and undervoltage sensing for the positive supply, VPP.
VNNSENSE (pin 38) performs the same function for the negative supply, VNN. When the current through
VPPSENSE (or VNNSENSE) goes below or above the values shown in the Electrical Characteristics
section (caused by changing the power supply voltage), the TDA1400 will be muted. VPPSENSE is
internally biased at 2.5V and VNNSENSE is biased at 1.25V. In a single-supply application, VNNSENSE
should be disabled by connecting a 16KΩ resistor for pin 38 to AGND.
Once the supply comes back into the supply voltage operating range (as defined by the supply sense
resistors), the TDA1400 will automatically be un-muted and will begin to amplify. There is a hysteresis
range on both the VPPSENSE and VNNSENSE pins. If the amplifier is powered up in the hysteresis
band, the amplifier will be muted. Therefore, the usable supply range is the difference between the over-
voltage turn-off and under-voltage turn-off for both the VPP and VNN supplies. It should be noted that the
supply voltage must be outside of the user defined supply range for greater than 200mS for the TDA1400
to be muted.
Figure 5 shows the proper connection for the Over / Under voltage sense circuit for both the VPPSENSE
and VNNSENSE pins.
V5
VNN
TDA1400
RVNN2
RVNN1
38
40
VNNSENSE
V5
VPP
RVPP2
RVPP1
VPPSENSE
Figure 5: Over / Under voltage sense circuit
The equation for calculating RVPP1 is as follows:
VPP
VPPSENSE
R
VPP1 =
I
Set RVPP2 = RVPP1 .
20
TDA1400 – Rev. 0.65/KLi/02.06
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
